Queued Commands

The VM-220 and later chips support a maximum burst data rate of 1.25 Mb/s.

This is made possible by a new hardware UART and queued commands handling in VM-220 and VM-300 chips and network integration in the newer BitScope models.

The original BitScope adopted a simple atomic and stateless Command Protocol where each command was echoed in acknowledgement. The host PC simply waited for the reply of the previous command to know when to proceed with the next one.

This was well suited to serial communications, made programming BitScope easy and data transfers reliable. However, tight hand-shake protocols such as this are not desirable when the communication takes place over packetized and fixed overhead transport mediums like Ethernet or USB.

BitScope command op-codes fall into two categories: simple commands for which a single reply byte (the command itself) is returned, and complex commands where the reply byte is followed by one or more data bytes (depending on the command).

The Network Adaptor allows multiple (simple) commands (and optionally one complex command) to be grouped together and sent in a single Command Packet between the PC and the adaptor. The adaptor feeds the commands to BitScope, checking the reply byte returned for each one, before sending a Reply Packet with all the acknowledgement bytes back to the PC.

If the last command in the group is a complex command, the data produced by the command is appended to the reply. If more data than one packet is produced, multiple packets are returned.